Waste heat collecting system having expansion device

ABSTRACT

An object of the invention is to provide a waste heat collecting system having an expansion device, in which an over expansion of refrigerant is prevented so that a loss to be caused by the over expansion is eliminated. A volume ratio of expansion for the expansion device is selected at a value, at which proper expansion of the refrigerant is achieved when the pressure difference between the high pressure and the low pressure is minimum.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application Nos. 2006-81426 filed on Mar. 23, 2006 and 2006-140295 filed on May 19, 2006, disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a waste heat collecting system having an expansion device, which is driven to rotate by expansion of high-pressure and high-temperature refrigerant to generate rotational driving force.

BACKGROUND OF THE INVENTION

According to a conventional technology, in which a rotational force is obtained by use of waste heat generated in a vehicle, refrigerant is heated by a heating device by use of heat generated in the vehicle to produce high pressure refrigerant. The high pressure refrigerant is supplied to a high pressure chamber of an expansion device, so that an output shaft is rotated by pressure difference between the high pressure chamber and a low pressure chamber of the expansion device. An output (work volume) of the expansion device is decided by “torque generated at the output shaft X a number of rotation”.

The expansion device gives a larger amount of the work volume, as the pressure difference between the high pressure in the high pressure chamber and the low pressure in the low pressure chamber becomes larger. Therefore, the refrigerant discharged from the low pressure chamber is cooled down by a condensing device.

Rankine cycle is known in the art as an apparatus for generating the rotational force by use of the pressure difference of the refrigerant, wherein the refrigerant is circulated in a circuit having a refrigerant pump, a heating device, an expansion device, and a condensing device.

When the Rankine cycle is mounted in the vehicle, the pressure difference between the high pressure side and the low pressure side varies depending on a change of the ambient temperature due to a change of seasons, even after warm-up of an engine is finished.

For example, the temperature of the engine cooling water is maintained at a value between 80° C. and 100° C., so that the pressure at the high pressure side is stably controlled at a constant value, in such a system in which the refrigerant is heated in a heating device by the engine cooling water (hot water) and the refrigerant is cooled down in a condensing device by the ambient air. On the other hand, the temperature of the ambient air varies in a range of 0° C. and 35° C. depending on the change of seasons. Therefore, the condensing capacity for the refrigerant varies so that the pressure at the low pressure side largely varies.

When a volume ratio of expansion for the expansion device is considered, an expansion efficiency becomes maximum when a proper expansion is obtained without causing any over expansion or any insufficient expansion of the refrigerant. The proper expansion of the refrigerant is realized at a pressure condition meeting a designed pressure ratio, in case of the expansion device of a fixed capacity type.

The volume ratio of expansion for the expansion device should be considered in view of the influences to be caused throughout the year. The volume ratio of expansion, at which a waste heat collecting efficiency becomes maximum, is selected in view of the change of the ambient temperature, because the pressure at the high pressure side is controlled at a constant value by the engine cooling water which is controlled at almost a constant temperature. Namely, such a volume ratio of expansion, at which the proper expansion is achieved at an average temperature throughout the year, is generally selected.

In the case that the volume ratio of expansion is selected in the above manner, the insufficient expansion may occur when the actual temperature is lower than the ambient temperature for the proper expansion, whereas the over expansion may occur when the actual temperature is higher than the ambient temperature for the proper expansion.

When the over expansion takes place, a loss is generated by such over expansion. As a result, the output of the expansion device is decreased and the necessary amount of the work volume may not be obtained, when the actual temperature is higher than the ambient temperature for the proper expansion.

For example, in a system or an apparatus, in which a motor generator is driven by the expansion device, a necessary amount of electric power may not be generated due to the loss caused by the over expansion, when the ambient temperature is high, for example, during the summer season.

It is, therefore, necessary to improve to decrease the loss caused by the over expansion.

It is proposed in the art, for example, as disclosed in Japanese Patent Publication No. H10-266980, that a bypass passage is provided for communicating a working chamber (an expansion chamber) with a low pressure side, wherein the working chamber is even in a process of expansion (namely, the expansion process is not yet finished). A valve device is further provided to open the bypass passage, when the pressure in the working chamber reaches a predetermined pressure (a pressure at which the over expansion may occur). As a result, the over expansion is prevented.

According to the above prior art, however, the expansion device becomes more complicated in structure, because the bypass passage and the valve device are provided in the expansion device. And the cost of the expansion device is also increased. In addition, a failure probability will be increased, in case that an additional device (the valve device) is provided.

Another conventional expansion device is known in the art, for example, as disclosed in Japanese Patent Publication No. H10-266980. According to such conventional expansion device, it is a scroll-type device such that an expansion chamber is formed between a fixed scroll and a movable scroll. In the expansion device, a control passage is provided for communicating the expansion chamber with a discharge space formed on a discharging side of the working fluid. A valve device is provided in the control passage for opening and closing the control passage in accordance with a pressure difference between the expansion chamber and the discharge space. In case that the pressure difference between the high pressure side and the low pressure side of the expansion device becomes lower than a predetermined value, the expansion chamber is expanded to such a volume, to which the working fluid can be expanded under such pressure difference. Then, when the pressure in the expansion chamber becomes lower than the pressure in the discharge space, the valve device is operated to open the control passage. As a result, the pressures in the expansion chamber and the discharge space are equalized to stop the further expansion of the working fluid. Accordingly, an operation of the over-expansion is prevented to achieve an efficient operation.

SUMMARY OF THE INVENTION

The present invention is made in view of the above problems. An object of the present invention is, therefore, to provide a waste heat collecting system having an expansion device, which is driven by the expansion of the refrigerant to generate the rotational driving force, wherein a loss to be caused by the over expansion of the refrigerant is suppressed without increasing a complicated structure of the expansion device and a cost increase.

Another object of the present invention is to provide a waste heat collecting system having an expansion device, in which the over expansion of the refrigerant is prevented to obtain a stable operation for the expansion.

According to a feature of the present invention, a waste heat collecting apparatus for a vehicle has: an engine cooling circuit, through which engine cooling water is circulated; and Rankine cycle having an expansion device, a condensing device, a refrigerant pump, and a heating device, which are connected in a closed circuit so that refrigerant is circulated in the closed circuit by the operation of the refrigerant pump.

The heating device is disposed in the engine cooling circuit for heating the refrigerant of the Rankine cycle with the heat of the engine cooling water, so that the refrigerant is converted to high pressure and high temperature refrigerant. The heating device is connected to an inlet side of the expansion device for supplying the high pressure refrigerant to the expansion device.

The condensing device is connected to an outlet side of the expansion device for cooling down and condensing the refrigerant from the expansion device through heat exchange with the ambient air, so that the pressure of the refrigerant at the outlet side of the expansion device depends on a condensing capacity of the condensing device.

The expansion device is of a fixed displacement type fluid machine, and an output shaft of the expansion device is driven to rotate by expansion of the refrigerant in a working chamber thereof, the expansion of the refrigerant is performed by a pressure difference of the refrigerant between the high pressure at the inlet side and low pressure at the outlet side of the expansion device.

A volume ratio of expansion for the expansion device is selected at a value, at which proper expansion of the refrigerant is achieved when the pressure difference between the high pressure and the low pressure is minimum.

According to another feature of the present invention, a waste heat collecting apparatus for a vehicle has Rankine cycle, which comprises: an expansion device; a condensing device; a refrigerant pump; and a heating device, wherein the expansion device, the condensing device, the refrigerant pump, and the heating device are connected in a closed circuit so that refrigerant is circulated in the closed circuit by the operation of the refrigerant pump, the expansion device generating a rotational driving force by expansion of the refrigerant.

The waste heat collecting apparatus further comprises: an electric power generator operatively connected to the expansion device for generating the electric power when it is driven to rotate by the rotational driving force of the expansion device; a pressure detecting device for detecting a pressure difference of the refrigerant between a pressure at a high pressure side of the expansion device and a pressure at a low pressure side of the expansion device; and a pressure increasing means for increasing the pressure difference when the pressure difference detected by the pressure detecting device is lower than a predetermined pressure difference, so that the pressure difference becomes closer to the predetermined pressure difference.

According to a further feature of the present invention, a rotational force generating apparatus has a high pressure generating device for generating a high pressure of working fluid; a low pressure generating device for generating a low pressure of the working fluid; and an expansion device having a fixed displacement and rotating an output shaft by a pressure difference of the working fluid between the high pressure generated by the high pressure generating device and the low pressure generated by the low pressure generating device.

In the rotational force generating apparatus, a volume ratio of expansion for the expansion device is selected at a value, at which proper expansion of the working fluid is achieved when the pressure difference between the high pressure and the low pressure is minimum.

According to a still further feature of the present invention, a control system for an expansion device has: an expansion device for generating a rotational driving force by expansion of high pressure and high temperature working fluid; an electric power generator driven by the rotational driving force of the expansion device; and a pressure detecting device for detecting a pressure difference of the working fluid between a pressure at a high pressure side of the expansion device and a pressure at a low pressure side of the expansion device.

The control system for the expansion device has a pressure increasing means for increasing the pressure difference when the pressure difference detected by the pressure detecting device is lower than a predetermined pressure difference, so that the pressure difference becomes closer to the predetermined pressure difference.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic diagram showing a structure of an engine cooling circuit, a refrigerating cycle, and Rankine cycle according to a first embodiment of the present invention;

FIG. 2 is a cross sectional view schematically showing a fluid machine;

FIG. 3 is an explanatory view showing a fixed scroll and a movable scroll, which are engaged with each other;

FIGS. 4A to 4C are P-V diagrams respectively showing a relation between a pressure applied to an expansion device and a volume of a working chamber;

FIG. 5 is a graph showing a relation between a volume ratio of expansion and a capacity ratio of the expansion with respect to ambient temperature;

FIG. 6 is a schematic diagram showing a system structure of a second embodiment of the present invention;

FIG. 7 is a flow chart showing a routine for carrying out an increase of a pressure difference in the second embodiment;

FIG. 8 is a schematic diagram showing a system structure of a third embodiment of the present invention;

FIG. 9 is a flow chart showing a routine for carrying out the increase of the pressure difference in the third embodiment;

FIG. 10 is a schematic diagram showing a system structure of a fourth embodiment of the present invention; and

FIG. 11 is a flow chart showing a routine for carrying out the increase of the pressure difference in the fourth embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

A system structure of a waste heat collecting apparatus will be explained with reference to FIG. 1. The waste heat collecting apparatus according to an embodiment of the present invention gets a rotational energy, by use of Rankine cycle 110, out of heat in engine cooling water (hot water) circulated in an engine cooling circuit 1, to generate electric power. As shown in FIG. 1, a part of the Rankine cycle 110 is commonly used in a refrigerating cycle 3 for an air conditioning apparatus mounted in an automotive vehicle.

The engine cooling circuit 1 has a main circuit, in which the engine cooling water is circulated from a radiator 4, a water pump 5, an engine (a water jacket), a heating device 111, and back to the radiator 4. The engine cooling circuit 1 has an air conditioning hot water circuit, in which the engine cooling water (hot water) is circulated from the engine (the water jacket), a heater core 8, and back to the engine. The heating device 111 is a component of the Rankine cycle 110, which will be below.

The radiator 4 cools down the engine cooling water through heat exchange between the engine cooling water and the external air, which is supplied to the radiator 4 by a vehicle travel and/or a radiator fan. A radiator bypass passage 4 a is provided to bypass a heat exchanging portion of the radiator 4, and a thermostat 4 b is provided for controlling a flow ratio between a flow amount to the heat exchanging portion and to the bypass passage 4 a. The thermostat 4 b has a valve, which opens and closes a fluid passage or changes an opening degree of the fluid passage in accordance with temperature of the engine cooling water, to control the flow amount of the engine cooling water flowing through the heat exchanging portion of the radiator 4. As a result, the temperature of the engine cooling water is stably controlled at a value between 80° C. and 100° C.

The water pump 5 is operated by the electric power from a battery 11 mounted in the vehicle or driven by an output of the engine 6, to circulate the engine cooling water in the engine cooling circuit 1.

The engine 6 is an internal combustion engine for producing a rotational force by combustion of fuel. The temperature of the engine 6 is controlled by the engine cooling water flowing through the water jacket formed in the engine 6, so that the temperature is controlled at a value within a predetermined range.

The heater core 8 is a heat exchanger provided in a unit casing 12 of the air conditioning apparatus for heating the air to be blown into a passenger room by a blower device 13, through heat exchange between the air and the engine cooling water.

The refrigerating cycle 3 has a closed circuit, through which refrigerant is circulated from a compressor 14, a condensing device 113, a receiver 16, a depressurizing device 17, an evaporator 18, and back to the compressor 14. An operation of the refrigerating cycle 3 is controlled by an electronic control unit (ECU) 133.

The compressor 14 is operatively connected to the engine 6 via an electromagnetic valve 14 b, a pulley 14 a, and a driving belt 22, so that the rotational driving force of the engine 6 is transmitted to the compressor 14. The compressor 14, accordingly, draws the refrigerant, and compresses and pumps out the same.

The condensing device 113 is a heat exchanger for cooling the high pressure and high temperature refrigerant from the compressor 14 through heat exchange with external air supplied thereto by the vehicle travel or by a condenser fan 142, so that the refrigerant is condensed and liquefied. The condenser fan 142 may be commonly used as the radiator fan.

The receiver 16 separates the refrigerant, which is condensed at the condensing device 113, into a liquid phase refrigerant and a gas phase refrigerant, and supplies the liquid-phase refrigerant to the depressurizing device 17.

The depressurizing device carries out an adiabatic expansion of the liquid-phase refrigerant separated at the receiver 16.

The evaporator 18 is arranged in the unit casing 12 of the air conditioning apparatus for cooling the air passing through the evaporator by heat exchange between atomized refrigerant and the air blown into the passenger room by the blower device 13. The atomized refrigerant is vaporized in the evaporator 18 by absorbing vaporization heat, so that the air passing through the evaporator 18 is cooled down.

The gas phase refrigerant vaporized in the evaporator 18 is sucked again into the compressor 14, so that the above operation is repeated so long as the compressor 14 is in operation.

The unit casing 12 has the blower device 13, which is operated by the electric power from the battery 11, the evaporator 18 for cooling down the air blown into the passenger room by the blower device 13, and the heater core 8 for heating the air.

A heater core bypass passage 23 is formed in the unit casing 12 and an air-mix door 24 is provided at an upstream side of the heater core 8 for controlling a ratio of the air flow, namely a ratio of the air flow between the air flowing through the heater core 8 and the air flowing through the heater core bypass passage 23. The air-mix door 24 is controlled manually or by an actuator controlled by the ECU 133. The temperature of the air blown into the passenger room is controlled by changing the ratio of the air flow by the air-mix door 24.

The Rankine cycle 110 is formed by a closed circuit, in which the refrigerant is circulated from the condensing device 113, the receiver 16, a refrigerant pump 114, the heating device 111, an expansion device 112, and back to the condensing device 113. An operation of the Rankine cycle 110 is controlled by the ECU 133.

The condensing device 113 and the receiver 16 are commonly used in the Rankine cycle 110 and the refrigerating cycle 3. And the refrigerant circulated in both cycles are the same to each other.

The condensing device 113 is provided at the downstream side of the expansion device 112 and cools down the refrigerant in the Rankine cycle 110. Therefore, the condensing device 113 functions as a low pressure generator for generating low pressure at an outlet side of the expansion device 112 and also functions as a heat exchanger for cooling down the refrigerant. The refrigerant at the inlet side of the condensing device 113 is at high pressure and high temperature when the refrigerating cycle 3 is in its operation, whereas the pressure of the refrigerant at the inlet side of the condensing device 113 is lower than that at the outlet side of the heating device 111 when the Rankine cycle 110 is in its operation.

The receiver 16 supplies the gas phase refrigerant to the refrigerant pump 114 during the operation of the Rankine cycle 110.

The refrigerant pump 114 is driven to rotate by an electric motor (a motor generator) 120 to pressurize and supply the refrigerant from the receiver 16 to the heating device 111. The motor generator 120 generates a rotational force to drive the refrigerant pump 114, when electric power is supplied from the battery 11 through an inverter 141. On the other hand, the motor generator 120 generates electric power when it is driven to rotate by the output of the expansion device 112.

The liquid phase refrigerant pressurized by the refrigerant pump 114 is heated at the heating device 111 by the heat exchange with the engine cooling water circulating in the main circuit of the engine cooling circuit. Therefore, the refrigerant is heated to super heated steam of the refrigerant, to which expansion energy is given. The heating device 111 works as a high pressure generating device for generating high pressure energy at the inlet side of the expansion device 112.

The expansion device 112 is a fixed capacitor type expansion device, an output shaft of which is rotated by the pressure difference between the high pressure and the low pressure. Namely, the super heated steam of the refrigerant passing through the heating device 111 is supplied to the inlet side of the expansion device 112, and the outlet side of the expansion device 112 is connected to the inlet side of the condensing device 113. Accordingly, the output shaft of the expansion device 112 is rotated by the pressure difference between the high pressure of the super heated steam of the refrigerant at the inlet side of the expansion device 112 and the low pressure generated at the condensing device 113 at the outlet side of the expansion device 112.

The output shaft of the expansion device 112 drives an input shaft of the motor generator 120. The output shaft of the expansion device 112, the input shaft of the motor generator 120, and a driving shaft of the refrigerant pump 114 are formed by a common shaft 29. Accordingly, when the expansion device 112 generates the rotational force, the motor generator 120 as well as the refrigerant pump 114 is rotated by such rotational force. On the other hand, when the rotational force is generated at the motor generator 120, the expansion device 112 as well as the refrigerant pump 114 is rotated by the rotational force.

The Rankine cycle 110 has a pressure equalization device 30, which opens or closes a communication between the high pressure side and the low pressure side of the expansion device 112. The pressure equalization device 30 is provided in the inside of the expansion device 112, as described below. It may be, however, provided at an outside of the expansion device 112. The pressure equalization device 30 makes the pressure difference smaller by communicating the high pressure side and the low pressure side of the expansion device 112 with each other, when the expansion device 112 is not operated or when the operation of the expansion device 112 is stopped.

The inverter 141 controls the operation of the motor generator 120. Namely, the inverter 141 controls the power supply from the battery 11 to the motor generator 120, when the motor generator 120 is operated as the electric motor, whereas the inverter controls the charging current from the motor generator 120 to the battery 11 depending on a charged condition thereof, when the motor generator 120 is operated as the electric power generator by the rotational force generated at the expansion device 112.

The ECU 133 controls, in addition to the above operation of the inverter 141, the electrical components for the Rankine cycle 110 and the refrigerating cycle 3. A power switch (for example, an ignition switch) 31 is provided to the ECU 133, to stop the operation of the ECU 133, the Rankine cycle 110, and the refrigerating cycle 3, by cutting off the power supply from the battery 11, when the power switch 31 is turned off.

The refrigerant pump 114, the expansion device 112, and the motor generator 120 are coaxially arranged and integrally formed as a fluid machine of a pump-expansion-generator device, as shown in FIG. 2.

The common shaft 29 is rotatably supported by first and second bearings 32 and 33 in the fluid machine.

The fluid machine has first to fifth housing parts 34 to 38, which are firmly connected with each other by, for example, bolts, in an axial direction.

The first housing part 34 accommodates the pressure equalization device 30, the second housing part 35 is used as a fixed scroll 41 of the expansion device 112, the third housing part 36 accommodates a movable scroll 42 of the expansion device 112 and the motor generator 120, the fourth housing part 37 accommodates the refrigerant pump 114, and the fifth housing part 38 closes an accommodating chamber for the refrigerant pump 114.

A part of the third housing part 36 is formed as a shaft housing 39 for supporting the first bearing 32.

The expansion device 112 has a structure similar to a well known scroll type compressor, in which inlet side and outlet side are reversed.

The expansion device 112 has the fixed scroll 41 integrally formed as the second housing part 35, the movable scroll 42 engaged with the fixed scroll 41 and rotated with an orbital motion, an auto-rotation preventing device 43 for preventing the auto-rotation of the movable scroll 42, and an output portion 44 for generating the rotational force from the orbital motion of the movable scroll 42.

The fixed scroll 41, which is integrally formed as the second housing part 35, has a base plate 41 a and a fixed scroll wrap 41 b.

A right-hand side of the base plate 41 a (in FIG. 2) is formed on a plane perpendicular to an axial direction, and a seal member formed at a forward end of a movable scroll wrap 41 b (described below) slides on the base plate 41 a.

The fixed scroll wrap 41 b is a vortical wrap extending in the axial direction from the base plate 41 a.

A high pressure chamber 45 is formed between the first and second housing parts 34 and 35. The high pressure chamber 45 is a space for communicating an inlet port 46 formed at the base plate 41 a with a high pressure port 47, through which the super heated steam of the refrigerant is introduced from the heating device 111.

A low pressure chamber 48 is formed in the inside of the third housing part 36. The low pressure chamber 48 is a space for communicating a space (referred to as a discharge portion 49) formed at an outer periphery of the fixed and movable scrolls 41 and 42 with a low pressure port 50, through which the refrigerant flows back to the condensing device 113. The motor generator 120 is accommodated in the above space.

The movable scroll 42 forms a pair with the fixed scroll 41 and rotates with respect to the fixed scroll 41 with the orbital motion. The movable scroll 42 is pushed toward the fixed scroll by the shaft housing 39, so that multiple working chambers (expansion chambers) V are formed by spaces surrounded by the fixed scroll 41 and the movable scroll 42, as shown in FIG. 3. A sliding plate 52 is interposed between the movable scroll 42 and the shaft housing 39, to enable a smooth rotation of the movable scroll 42.

The movable scroll 42 has a base plate 42 a and a movable scroll wrap 42 b.

A left-hand side of the base plate 42 a (in FIG. 2) is formed on a plane perpendicular to the axial direction, and a seal member formed at a forward end of the fixed scroll wrap 41 b slides on the base plate 42 a.

The movable scroll wrap 42 b is a vortical wrap extending in the axial direction from the base plate 42 a. As shown in FIG. 3, the movable scroll wrap 42 b is engaged with the fixed scroll wrap 41 b at such a position, in which the movable scroll 42 is displaced by an angle of 180° with respect to the fixed scroll 41.

When the movable scroll 42 rotates with the orbital motion, the working chamber V surrounded by the fixed and movable scrolls 41 and 42 moves from a center portion to an outer periphery, and a volume of the working chamber V is increased in accordance with the above movement to the outer periphery. When the super heated steam of the refrigerant is introduced from the inlet port 46 into the working chamber V at the center portion, the expansion energy of the super heated steam works to expand the volume of the working chamber V. When the movable scroll 42 is rotated by the above expanding energy in the working chamber V, the movable scroll 42 is rotated by the orbital motion. When the working chamber V moves to the outer periphery of the scrolls 41 and 42, and the working chamber V is communicated with the discharge portion 49, the refrigerant is discharged from the working chamber V to the low pressure chamber 48.

The auto-rotation preventing device 43 (a crank device 43) prevents the auto-rotation of the movable scroll 42, in order to achieve the orbital motion. The auto-rotation preventing device 43 has a pin 51 fixed to the movable scroll 42 and extending in the axial direction, and a groove 51 a formed in the shaft housing 39 and extending in a radial direction, wherein the pin 51 is engaged in the groove 51 a in order to prevent the auto-rotation but to allow the orbital motion of the movable scroll 42.

The output portion 44 generates the rotational force from the orbital motion of the movable scroll 42, as already explained, and has a cylindrical boss 53 and an eccentric shaft portion 54. The cylindrical boss 53 is integrally formed with the movable scroll 42, extending from the base plate 42 a in the right-hand direction. The eccentric shaft portion 54 is formed at a left-hand end of the common shaft 29, wherein the shaft portion 54 is eccentric to the rotating center of the common shaft 29. The eccentric shaft portion 29 is inserted into an inside of the cylindrical boss 53 and rotationally connected with the cylindrical boss via a bearing 55.

According to the above structure, the cylindrical boss 53 rotates with the orbital motion together with the movable scroll 42, and the eccentric shaft portion 54 is rotated together with the common shaft 29.

As above, the orbital motion of the movable scroll 42 caused by the expanding energy of the refrigerant is converted into the rotation of the common shaft 29 through the rotation of the eccentric shaft portion 54.

The pressure equalization device 30 communicates or cuts off the communication between the high pressure side and the low pressure side of the expansion device 112. A major portion of the pressure equalization device 30 is accommodated in the first housing part 34.

The pressure equalization device 30 has a bypass passage 56, a valve device 57, and an electromagnetic valve 58. The bypass passage 56 is a communication passage formed in the second housing part 35 for connecting the high pressure chamber 45 with the discharge portion 49.

The valve device 57 has a piston 57 a slidably inserted into a cylinder formed in the first housing part 34 and extending in the axial direction. The valve device 57 further has a valve body 57 b connected to the piston 57 a to open and close the bypass passage 56. A compression coil spring 57 d is inserted into a back pressure chamber 57 c formed by the cylinder for biasing the piston 57 a in a valve closing direction (in a direction to close the bypass passage 56). The bypass passage 56 is closed by the valve body 57 b, when the pressure in the back pressure chamber 57 c is increased.

The electromagnetic valve 58 is operated by the ECU 133 to control the pressure in the back pressure chamber 57 c. When the electric power is supplied to the electromagnetic valve 58, the high pressure is supplied from the high pressure chamber 45 to the back pressure chamber 57 c, whereas the low pressure is supplied from the low pressure chamber 48 to the back pressure chamber 57 c when the power supply to the electromagnetic valve 58 is cut off.

Therefore, when the electric power is supplied to the electromagnetic valve 58, the pressure in the back pressure chamber 57 c is increased so that the valve body 57 b is strongly pushed together with the spring force of the spring 57 d to the bypass passage 56, to close the bypass passage 56. The communication between the high pressure chamber 45 and the low pressure chamber 48 through the bypass passage 56 is cut off.

On the other hand, when the power supply to the electromagnetic valve 58 is cut off, the pressure in the back pressure chamber 57 c is decreased so that the piston 57 a compresses the spring 57 d by the pressure in the high pressure chamber 45. The valve body 57 b is moved in the leftward direction to open the bypass passage 56. Accordingly, the high pressure chamber 45 and the low pressure chamber 48 are communicated with each other through the bypass passage 56, to equalize the pressure in the high pressure side and low pressure side.

The motor generator 120 has a stator 61 and a rotor 62. The stator 61 has a stator core 61 a fixed to an inner peripheral surface of a motor housing 36 a formed by the third housing part 36, and a stator coil 61 b wound on the stator core 61 a. The rotor 62 has permanent magnets firmly inserted and held in a rotor core mounted to the common shaft 29.

When the electric power is supplied to the stator coil 61 b through the inverter 141, the rotor 62 and the common shaft 29 are driven to rotate. On the other hand, when the common shaft 29 is rotated, the electric power is generated at the stator coil 61 b by the rotation of the rotor 62.

More exactly, the electric power is supplied to the stator coil 61 b from the battery 11 through the inverter 141 at a start-up operation of the Rankine cycle 110. The rotor 62 is thereby driven to rotate, to operate the motor generator 120 as the electric motor for driving the expansion device 112 and the refrigerant pump 114.

On the other hand, when the expansion device 112 is in its operation, the refrigerant pump 114 and the rotor 62 are driven to rotate by the rotational driving force generated at the expansion device 112, so that the motor generator 120 is operated as the electric power generator. The electric power generated at the motor generator 120 is charged into the battery 11.

The refrigerant pump 114 is a rolling piston type pump arranged in the fourth housing part 37, and has a pump housing 63, an eccentric cam 64, a pump rotor 65, and a vane 66.

The pump housing has an cylindrical center housing 63 a and first and second side housings 63 b and 63 c, which are connected to the fourth housing part 37 by a fixing means, such as bolts. The first side housing 63 b supports the second bearing 33.

The eccentric cam 64 is formed at a right hand end of the common shaft 29. The eccentric cam 64 having a circular cross section is eccentric to the rotating center of the common shaft 29, and accommodated in the inside of the center housing 63 a. The pump rotor 65 is an annular member provided at an outer periphery of the eccentric cam 64. An outer diameter of the pump rotor 65 is smaller than an inner diameter of the center housing 63 a. The pump rotor 65 rotates with an orbital motion within the space of the center housing 63 a, in accordance with the rotation of the eccentric cam 64.

A lubricating passage 29 a is formed in the common shaft 29 for introducing the refrigerant (together with lubricating oil contained in the refrigerant) from the low pressure chamber 48 to the inside of the pump rotor 65. An orifice 29 a is formed at an end of the lubricating passage 29 a, at a side to the pump rotor 65.

The vane 66 is slidably supported by the center housing 63 a in a radial direction and biased by a spring (not shown) inwardly in the radial direction. The vane 66 defines a pump chamber P between the pump rotor 65 and the center housing 63 a.

A pump inlet port 67 and a pump outlet port (not shown) are respectively formed at both sides of the pump rotor 65, adjacent to the vane 66. A pump inlet pipe 68 connected to the pump inlet port 67 is provided at the fourth housing part 37, which accommodates the refrigerant pump 114. The pump inlet pipe 68 is connected, at the other end thereof, to an outlet port of the receiver 16 for the liquid phase refrigerant.

The pump outlet port (not shown) is communicated with a pump discharge chamber 69, which is formed in the fourth housing part 37 for accommodating the refrigerant pump 114. A pump outlet pipe 71 is provided in the fourth housing part 37 for communicating the pump discharge chamber 69 with the inlet side of the heating device 111. A check valve 72 is provided at an opening portion of the pump outlet port, which opens to the pump discharge chamber 69, so that the refrigerant is allowed to flow only in a direction from the pump outlet port to the pump discharge chamber 69.

In the refrigerant pump 114, the refrigerant is sucked into the pump chamber P from the pump inlet pipe 68 through the pump inlet port 67, in accordance with the rotation (the orbital motion) of the pump rotor 65 driven by the common shaft 29. The refrigerant is then pumped out from the pump chamber P to the pump outlet pipe 71 through the pump outlet port (not shown) and the pump discharge chamber 69.

An operation of the Rankine cycle will be explained. The ECU 133 starts the operation of the Rankine cycle 110, when the ECU 133 determines that the charged amount of the electric power in the battery is lower than a predetermined value and that it is in a condition that the operation of the Rankine cycle is possible (namely, when the temperature of the engine cooling water is higher than a predetermined temperature). More specifically, the current supply to the electromagnetic valve 58 is cut off during a period shortly after the start-up of the Rankine cycle 110, so that the bypass passage 56 is opened by the valve device 57. And the motor generator 120 is operated as the electric motor to drive the refrigerant pump 114 and the expansion device 112.

In this operation, the refrigerant pump 114 sucks the refrigerant from the receiver 16 and pumps out the pressurized refrigerant to the heating device 111. The refrigerant is heated at the heating device 111 through the heat exchange with the engine cooling water and supplied into the expansion device 112. The refrigerant introduced into the expansion device 112 through the high pressure port 47 directly flows from the high pressure chamber 45 to the low pressure chamber 48 through the bypass passage 56, because the bypass passage 56 is opened by the high pressure refrigerant introduced into the high pressure chamber 45. Then, the refrigerant returns to the inlet side of the condensing device 113 through the low pressure port 50.

When a predetermined time (a time during which the refrigerant is sufficiently heated at the heating device 111 to super heated steam of the refrigerant) has passed by since the motor generator 120 had been operated as the electric motor, the ECU 133 turns on the electromagnetic valve 58 to close the bypass passage 56 by the valve device 57. As a result, the super heated steam of the refrigerant in the high pressure chamber 45 is introduced into the working chamber V through the inlet port 46.

The super heated steam of the refrigerant introduced into the working chamber V at the center portion increases the volume of the working chamber V by its expanding energy, so that the movable scroll 42 is rotated with the orbital motion. The working chamber V moves from the center portion to the outer periphery, as the volume of the working chamber V is increased. When the working chamber V becomes in communication with the discharge portion 49, the refrigerant flows from the working chamber V to the low pressure chamber 48. The refrigerant returns to the inlet side of the condensing device 113 through the low pressure port 50, so that the refrigerant is circulated through the condensing device 113, the receiver 16, the refrigerant pump 114, the heating device 111, and the expansion device 112.

The orbital movement of the movable scroll 42 is converted into the rotation at the output portion 44 to rotate the common shaft 29. The refrigerant pump 114 and the motor generator 120 are thereby driven to rotate.

When the rotational driving force of the expansion device 112 reaches such a value, at which the refrigerant pump 114 can be rotated in a normal condition, the ECU 133 switches over the operation of the motor generator 120 from the electric motor to the power generator, so that the electric power generated at the motor generator 120 is charged into the battery 11 through the inverter 141.

The ECU 133 cuts off the electric power supply to the electromagnetic valve 58, when the charged amount in the battery 11 reaches a predetermined charge amount or when the ECU 133 determines any abnormal condition. Then, the bypass passage 56 is opened to equalize the pressure at the inlet side and the outlet side of the expansion device 112, because the super heated steam of the refrigerant supplied to the high pressure chamber 45 flows to the low pressure chamber 48 through the bypass passage 56. The rotation of the expansion device 112 is stopped as a result of the decrease of the pressure difference between the inlet and outlet sides thereof, so that the operation of the Rankine cycle 110 is stopped.

In the above Rankine cycle 110, the high pressure to be applied to the expansion device 112 is obtained by the super heated steam of the refrigerant, which is heated by the engine cooling water. The temperature of the engine cooling water is maintained at a temperature of 80° C. to 100° C., by the operation of the thermostat 4 b. Therefore, the high pressure applied to the expansion device 112 is stable throughout one year.

On the other hand, the low pressure to be applied to the expansion device 112 changes depending on the condensing capacity of the condensing device 113. The condensing capacity of the condensing device 113 changes in accordance with a change of ambient temperature. Accordingly, the low pressure applied to the expansion device 112 largely changes even during a normal constant operation after a warming-up operation of the Rankine cycle 110.

A volume ratio of expansion for the expansion device 112 should be decided under the consideration of circumstances throughout the year, in case of the fixed capacitor type expansion device.

The volume ratio of the expansion is expressed by the following formula: Volume ratio=Vout1/Vin1=Vout2/Vin2,

wherein “Vin1” or “Vin2” is a volume of the working chamber V formed at the center portion (the high pressure side) shortly after the inlet port 46 is closed, whereas “Vout1” or “Vout2” is the volume of the working chamber V formed at the outer periphery shortly before the working chamber V is communicated with the discharge portion 49, as indicated in FIG. 3.

The volume ratio of the expansion is generally selected at such a value, at which energy collecting efficiency is maximum. When the high pressure to the expansion device 112 is constant due to the constant temperature of the engine cooling water, the variation of the ambient temperature should be taken into consideration. Namely, the volume ratio of the expansion is selected based on an average temperature throughout the year, at such a value at which a proper expansion is realized.

In the case that the volume ratio for the proper expansion is selected as above, an over expansion or an insufficient expansion may not occur at a predetermined ambient temperature, at which the proper expansion is realized, as shown in FIG. 4B.

However, the insufficient expansion occurs, as shown in FIG. 4C, when the ambient temperature is lower than the predetermined ambient temperature for the proper expansion. And the over expansion occurs, as shown in FIG. 4A, when the ambient temperature is higher than the predetermined ambient temperature for the proper expansion.

A hatched area A in each of FIGS. 4A to 4C shows an actual expanding power (energy), which is obtained at the expansion device 112 by the flow-in, the expansion, and the flow-out of the super heated steam of the refrigerant. An area surrounded by a dotted line B in each of FIGS. 4A to 4C shows a theoretical expanding power. A white area C shows a power lost. PH designates the pressure at the high pressure side of the expansion device 112, and PL designates the pressure at the low pressure side of the expansion device 112.

As shown in FIG. 4A, there is a loss caused by the over expansion, when the over expansion of the refrigerant takes place. When the ambient temperature is very much high, for example, in the summer season, a necessary amount of the electric power may not be obtained at the motor generator 120 because of the loss caused by the over expansion.

In the conventional system, a priority is given to get the maximum work volume out of the heat of the engine cooling water. However, it is more preferable to constantly generate the electric power necessary for the vehicle than to increase the amount of the generated electric power, in the case that the electric power is generated.

In other words, it is more preferable to suppress the loss and to get the necessary electric power in the circumstance of the high ambient temperature, such as in the summer season, than to get the maximum generated amount of the electric power throughout the year.

According to the above embodiment, however, the volume ratio of the expansion is decided as below. The pressure difference between the high pressure side and the low pressure side of the expansion device 112 varies in a certain range, even when the Rankine cycle 110 is in the constant operation after the warming-up operation for the engine 6 has been ended. The volume ratio of the expansion for the expansion device 112 is selected at such a value, at which the proper expansion is realized (in other words, the over expansion or the insufficient expansion may not occur) even when the pressure difference is at its minimum amount within the above range.

More exactly, the pressure is almost constant at the high pressure side of the expansion device 112 throughout the year, but the pressure at the low pressure side varies depending on the change of the ambient temperature, so that the pressure difference between the high pressure side and the low pressure side becomes smaller in the summer season. The volume ratio of the expansion for the expansion device 112 is selected at such a value, at which the proper expansion is realized (in other words, the over expansion or the insufficient expansion may not occur) even at the highest ambient temperature in the daytime of the summer season, for example, at an estimated road temperature in, the daytime of the summer season, at an estimated highest temperature in the daytime of the summer season, or an average temperature of the highest temperatures of the day for a period of one month in which the average temperature is the highest among the months.

According to the above embodiment, the condensing device 113 is commonly used for the Rankine cycle 110 and the refrigerating cycle 3, so that the condensing capacity for the refrigerant is relatively large. The refrigerant for the Rankine cycle 110 is the same to that for the refrigerating cycle 3, for example, HFC, HC or the like.

In the above Rankine cycle 110, the pressure at the high pressure side of the expansion device 112 is stably maintained at a value between 2.0 MPa and 2.5 MPa, because the temperature of the engine cooling water is stably maintained at the value between 80° C. to 100° C.

On the other hand, the ambient temperature, which affects the condensing capacity of the condensing device 113, largely varies throughout the year. The pressure at the low pressure side (the outlet side) of the expansion device 112 is increased to 1.1 MPa, when the ambient temperature is 30° C., whereas the pressure at the low pressure side (the outlet side) of the expansion device 112 is decreased to 0.5 MPa, when the ambient temperature is 0° C.

A relation between the volume ratio of the expansion and a capacity ratio of the expansion, with respect to the ambient temperature (5° C. to 30° C.), is shown in FIG. 5.

As shown in FIG. 5, the proper expansion can be achieved at the volume ratio of the expansion which is around 2, when the ambient temperature is high (at 30° C.). The volume ratio of the expansion, at which the proper expansion will be achieved, is increased, as the ambient temperature is decreased.

According to the above embodiment, the volume ratio of the expansion for the expansion device 112 is selected at the value, at which the proper expansion (no over expansion, no insufficient expansion) is achieved in the summer season. More exactly, the pressure at the high pressure side is between 2.0 MPa to 2.5 MPa, the pressure at the low pressure side is around 1.1 Mpa, and the volume ratio of the expansion is about 2.0.

Namely, the volume ratio of the expansion for the expansion device 112 is selected at the value, at which the proper expansion is achieved at the high ambient temperature (for example, at the temperature between 30° C. and 35° C.) in the summer season. The volume ratio of the expansion is preferably selected at a value between 1.8 and 2.2, and most preferably at the value of 2.0.

According to the waste heat collecting apparatus of the above embodiment, the volume ratio of the expansion for the expansion device 112 is selected at such a value, at which the proper expansion is carried out at a side of the smaller pressure difference, within a range of variation for the pressure difference. Namely, the volume ratio of the expansion is selected at the value in a range of 1.5 and 2.5, at which the proper expansion is carried out in the summer season, in which the pressure at the low pressure side becomes higher. The pressure at the low pressure side varies depending on the change of the ambient temperature.

According to the above structure, the over expansion in the expansion device 112 can be prevented, even when the pressure at the low pressure side is increased as a result of the increase of the ambient temperature. As a result, a stable operation for the electric power generation can be realized within a wide range of the temperature, in which the vehicle is actually used.

Furthermore, as the volume ratio of the expansion is selected at such value, at which the proper expansion is carried out in the summer season, a stable amount of the electric power is generated throughout the year. And the conventional bypass passage and the valve device, which are required in the prior art, are no longer necessary.

The generation of the loss caused by the over expansion can be prevented, without causing the complicated structure and increase of the cost for the expansion device 112. The necessary amount of the electric power for the vehicle can be generated throughout the year. A failure probability for the expansion device 112 is decreased as a result of the simple structure of the expansion device 112, and thereby a reliability of the Rankine cycle 110 can be increased.

The above explained embodiment may be modified in various ways, as in the following manner.

The refrigerant pump 114, the expansion device 112, and the motor generator 120 are integrally formed in the single fluid machine. However, those components may be respectively formed as independent fluid machines.

The refrigerant pump is driven by the expansion device 112. However, the refrigerant pump 114 may be driven by an electric motor exclusively provided for the refrigerant pump.

The motor generator 120 is driven to rotate by the expansion device 112. However, any other components, such as a blower fan device, a supercharger device, the compressor 14, and so on may be driven by the expansion device 112.

Furthermore, the rotational force of the expansion device 112 may be charged or stored as a kinetic energy in a spring, a flywheel, and the like.

Some of the components are commonly used for the Rankine cycle 110 and the refrigerating cycle 3. The Rankine cycle 110 and the refrigerating cycle 3 may be formed as the independent cycles.

In the above embodiment, the waste heat from the engine (the heat in the engine cooling water) is used to heat the refrigerant to obtain the high pressure energy. The refrigerant maybe, however, heated by the waste heat, such as the heat in exhaust gas of the engine 6, the heat generated at the battery 11, the heat generated at the inverter 141, the heat in compressed air by a supercharger, and so on.

The refrigerant may be, furthermore, heated by combustion energy by a burner, the solar heat, and so on.

In the above embodiment, the Rankine cycle 110 is used for collecting the waste heat to convert the collected heat into the rotational force. Any other device than the Rankine cycle 110 may be used for operating the expansion device 112, which is driven by the pressure difference.

In the above embodiment, the refrigerant is cooled down by the external air, to generate the low pressure. The engine cooling water may be used to cool down the refrigerant, when the heating capacity for heating the refrigerant is large, for example in case of heating the refrigerant by exhaust gas of the engine 6.

In such a case, the pressure at the low pressure side will become stable, whereas the pressure at the high pressure side varies. Therefore, the volume ratio for the expansion is selected at the value, at which the proper expansion is achieved even when the pressure at the high pressure side is decreased within a range of variation for the pressure difference.

Second Embodiment

A second embodiment of the present invention will be explained with reference to FIGS. 6 and 7. A structure will be explained with reference to FIG. 6. The second embodiment shows a control system for an expansion device, which is applied to an expansion device 112 to be used in Rankine cycle 110 to be mounted in an automotive vehicle.

The vehicle, to which the present invention is applied, is a general passenger car, which is equipped with a water-cooled internal combustion engine (not shown) as a driving source for a vehicle travel. An alternator 150 is mounted in the vehicle, which is driven by the engine to generate electric power. The electric power generated by the alternator 150 is charged into a battery 11 through an inverter 141, and the electric power charged in the battery 11 is supplied to vehicle electrical loads 160, such as head lamps, a wiper motor, an audio equipment, and so on.

The Rankine cycle 110 collects waste heat (thermal energy of engine cooling water) generated at the engine, to convert the waste energy into electric energy and to use it. The Rankine cycle 110 has a liquid pump 114, a heating device 111, the expansion device 112, and a condensing device 113, wherein those components are connected in a closed circuit.

The pump 114 is a fluid machine driven by an electric motor (not shown) for circulating refrigerant (the working fluid) in the Rankine cycle 110. An operation of the electric motor is controlled by a pump inverter (not shown).

The heating device 111 is a heat exchanger having two fluid passages formed in the inside thereof, wherein the refrigerant from the pump 114 and high-temperature engine cooling water flows through the respective fluid passages. The heating device 111 heats the refrigerant through a heat-exchange between the refrigerant and the engine cooling water, so that the refrigerant is heated to high-pressure and high-temperature super heated steam of the refrigerant.

The expansion device 112 is a fluid machine for producing a rotational driving force by expansion of the super heated steam of the refrigerant heated by the heating device 111. The expansion device 112 is formed as the scroll type expansion device having a fixed scroll and a movable scroll.

An expansion chamber is formed between the fixed scroll and the movable scroll, wherein the movable scroll is rotated with respect to the fixed scroll with an orbital motion when the super heated steam of the refrigerant is expanded in the expansion chamber. A crank device is provided at the movable scroll, so that the rotational driving force can be taken out in accordance with the orbital motion of the movable scroll.

The crank device has a driving pin, which is eccentric to a shaft, and a cylindrical bushing having a hole eccentric to the shaft. The crank device biases the movable scroll toward the fixed scroll during the expansion of the refrigerant.

The condensing device 113 is a heat exchanger for condensing and liquefying the refrigerant through the heat-exchange with cooling air. A blower device 142 is provided to the condensing device 113 for supplying the cooling air toward a heat-exchange portion of the condensing device 113. An outlet side of the condensing device 113 is connected to the liquid pump 114.

A pressure sensor 131 of a high pressure side is provided at an inlet side of the expansion device 112, that is between the heating device 111 and the expansion device 112, for detecting refrigerant pressure of the high pressure side of the Rankine cycle 110 (hereinafter also referred to as a high pressure side pressure P1). A pressure signal detected at the pressure sensor 131 is outputted to a controller 133 (described below).

A pressure sensor 132 of a low pressure side is provided at an outlet side of the expansion device 112, that is between the expansion device 112 and the condensing device 113, for detecting refrigerant pressure of the low pressure side of the Rankine cycle 110 (hereinafter also referred to as a low pressure side pressure P2). A pressure signal detected at the pressure sensor 132 is likewise outputted to the controller 133.

The controller 133 has a calculating portion for calculating a pressure difference ΔP at the expansion device 112, which is a difference between the high pressure side pressure P1 and the low pressure side pressure P2 respectively detected at the pressure sensors 131 and 132. The calculated pressure difference ΔP is outputted to the inverter 141.

An electric power generator 120 (e.g. a synchronous generator) is connected to the expansion device 112. The electric power generator 120 is, for example, a three-phase alternating current generator, which has a rotor 121 (for example, a rotor having permanent magnets) connected to the crank device (the shaft) of the expansion device 112, and a stator 122 having a three-phase coil arranged at an outer periphery of the rotor 121. The electric power generator 120 generates electric current at the stator 122 in accordance with rotation of the rotor 121 driven by the rotational driving force of the expansion device 112.

An operation of the above generator 120 is controlled by the inverter 141 connected to the stator 122. Namely, the inverter 141 controls the electric current at the stator 122 to control the rotational speed of the rotor 121 during an operation of the electric power generation at the generator 120. Accordingly, the amount of electric power generated is controlled. The electric power generated is charged into the battery 11. The inverter 141 controls the rotational speed of the rotor 121 in accordance with the pressure difference ΔP supplied from the controller 133.

An operation of the control system for the expansion device (the Rankine cycle 110) will be explained with reference to a flow chart shown in FIG. 7.

The liquid pump 114 and the blower device 142 are activated to start the operation of the Rankine cycle 110, when the temperature of the engine cooling water becomes higher than a predetermined temperature so that a sufficient amount of waste heat can be obtained from the engine.

More in detail, the liquid phase refrigerant from the condensing device 113 is pressurized by the liquid pump 114 and supplied to the heating device 111. The liquid phase refrigerant is heated at the heating device 111 to the super heated steam of the refrigerant through the heat exchange with the high temperature engine cooling water. The super heated steam of the refrigerant is supplied to the expansion device 112. The super heated steam of the refrigerant is expanded and depressurized in the expansion device in an isentropic manner. As a result, the movable scroll is rotated with the orbital motion to generate the rotational driving force through the crank device connected to the movable scroll. The electric power generator 120 is driven by the rotational driving force, and the electric power generated at the generator 120 is charged into the battery 11 through the inverter 141. The electric power charged in the battery is used for the electrical loads 160 of the vehicle. As a result, a load to the alternator 150 is decreased. The refrigerant depressurized in the expansion device 112 is condensed and liquefied in the condensing device 113, and sucked into the liquid pump 114.

In the above operation of the Rankine cycle 110, a pressurizing capacity of the liquid pump 114 is adjusted in consideration of a heating capacity at the heating device 111 and a condensing capacity at the condensing device 113. Further, the pressurizing capacity of the liquid pump 114 is adjusted such that the pressure difference ΔP at the expansion device 112 is controlled at a predetermined pressure difference ΔPth (also referred to as a preset pressure difference), which is necessary for the expansion device 112 and the electric power generator 120 to achieve a target rotational speed for the efficient operation (power generation).

In the case that the respective capacities for the heating device, the condensing device and so on become off-balanced due to any reason during the operation of the Rankine cycle 110, the actual pressure difference ΔP may become lower than the predetermined pressure difference ΔPth. If it happened, an operation of an over-expansion would take place in the expansion device 112. Accordingly, the rotational speed of the electric power generator 120 is actively controlled in accordance with the pressure difference ΔP detected by a pressure detecting device 130 (the pressure sensors 131 and 132).

As shown in FIG. 7, the controller 133 (the inverter 141) starts the operation of the Rankine cycle 110 at a step S100. The controller 133 determines at a step S110 whether the pressure difference ΔP is lower than the predetermined pressure difference ΔPth. As already explained above, the pressure difference ΔP is calculated by the controller 133 based on the high pressure side pressure P1 and the low pressure side pressure P2 detected by the pressure sensors 131 and 132. The controller 133 controls the inverter 141, at a step S120, such that the rotational speed of the electric power generator 120 is decreased by a predetermined amount, when the pressure difference ΔP is lower than the predetermined pressure difference ΔPth.

In the case of NO at the step S110, namely when the pressure difference ΔP is higher than the predetermined pressure difference ΔPth, the controller 133 controls the inverter 141, at a step S130, so that the rotational speed of the electric power generator 120 is controlled at the target rotational speed. The process goes back to the step S110 from the step S120 or S130, to repeat the above operation.

As above, the rotational speed of the electric power generator 120 is decreased at the step S120. The rotational speed of the expansion device 112 is correspondingly decreased. Since the expansion device 112 works as a fluid flow resistance to the refrigerant, which is circulated in the Rankine cycle 110, the high pressure side pressure P1 of the expansion device 112 can be increased Accordingly, the pressure difference ΔP is increased toward the predetermined pressure difference ΔPth. As above, since the actual pressure difference ΔP is controlled at the value higher than the predetermined pressure difference ΔPth, the operation of the over-expansion at the expansion device 112 can be prevented, and a stable expanding operation can be realized.

The expansion device 112 is formed as the scroll type expansion device having the crank device for preventing an auto-rotation of a movable scroll. In the scroll type expansion device 112 having the crank device, a magnitude relation between the pressure in the working chamber (the expansion chamber) and the pressure in a discharge space for the refrigerant is repeatedly reversed by the operation of the crank device, when the over expansion takes place. Then, the movable and fixed scrolls are separated from or brought into contact with each other, to thereby generate chattering noise. Furthermore, in the operation of the over expansion of the scroll type expansion device 112, a force for biasing the movable scroll toward a thrust plate of the fixed scroll becomes smaller so that the movable scroll may be inclined against the fixed scroll. As a result, a slanted wear may be caused. As above, in the scroll type expansion device 112 having the crank device, to suppress the over expansion is extremely effective for preventing the generation of the chattering noise and the slanted wear.

When the pressure difference ΔP becomes lower than the predetermined pressure difference ΔPth, exciting current of the electric power generator 120 may be increased to increase magnetic flux density, as the means for increasing the pressure difference ΔP, in place of the inverter 141 of the electric power generator 120 (the means for decreasing the number of rotation). Namely, the rotor 121 of the electric power generator 120 is formed by the electric coil, instead of the permanent magnets, the magnetic flux density is increased by increasing the exciting current to such electric coil. As a result, the necessary torque for the electric power generator 120 is increased to thereby decrease the number of rotation. Accordingly, the pressure difference ΔP can be increased.

Third Embodiment

A third embodiment of the present invention is shown in FIGS. 8 and 9. In the third embodiment, the condensing device 113 and the blower device 142 are formed as the means 140A for increasing the pressure difference ΔP. The same reference numerals are used in the third embodiment to designate the same or similar components and parts in the third embodiment.

The blower device 142 of the third embodiment is formed as an electrical blower device for blowing the cooling air to the condensing device 113, as shown in FIG. 8. A rotational speed of the electrical blower device 142 is controlled by the controller 133. An operation of the third embodiment will be controlled by a flow chart shown in FIG. 9. In FIG. 9, the steps S120 and S130 of FIG. 7 are replaced by steps of S120A and S130A.

When the controller 133 determines, at the step S110, that the pressure difference ΔP at the expansion device 112 is lower than the predetermined pressure difference ΔPth, the controller 133 controls to increase the rotational speed of the blower device 142 by a predetermined rotational speed. Namely, the amount of the cooling air to be supplied to the condensing device 113 is increased by a predetermined amount.

In the case of NO at the step S110, namely when the pressure difference ΔP is higher than the predetermined pressure difference ΔPth, the controller 133 controls the blower device 142, at a step S130A, so that the rotational speed of the electric blower device 142 is controlled at the target rotational speed. The process goes back to the step S110 from the step S120A or S130A, to repeat the above operation.

As above, the operation for condensing the refrigerant is facilitated in the condensing device 113, when the rotational speed of the blower device 142 is increased at the step S120A, so that the pressure P2 at the low pressure side is decreased. As a result, the pressure difference ΔP is increased to become close to the predetermined pressure difference ΔPth. The over expansion of the expansion device 112 is likewise prevented, as in the same manner to the third embodiment. And the stable expansion operation can be achieved based on the predetermined pressure difference ΔPth.

Fourth Embodiment

A fourth embodiment of the present invention is shown in FIGS. 10 and 11. In the fourth embodiment, the liquid pump 114, an electric motor 143 for driving the liquid pump 114, and an inverter 144 for controlling the electric motor 143 are formed as the means 140B for increasing the pressure difference ΔP. The inverter 144 reads the pressure difference ΔP from the controller 133 to control the electric motor 143. The same reference numerals are used in the fourth embodiment to designate the same or similar components and parts in the second embodiment.

An operation of the fourth embodiment will be controlled by a flow chart shown in FIG. 11. In FIG. 11, the steps S120 and S130 of FIG. 7 are replaced by steps of S120B and S130B.

When the controller 133 determines, at the step S110, that the pressure difference ΔP at the expansion device 112 is lower than the predetermined pressure difference ΔPth, the controller 133 controls to increase the rotational speed of the electric motor 143 through the inverter 144 by a predetermined rotational speed. Namely, a pressurizing capacity of the liquid pump 114 is increased by a predetermined amount.

In the case of NO at the step S110, namely when the pressure difference ΔP is higher than the predetermined pressure difference ΔPth, the controller 133 controls the electric motor 143, at a step S130B, so that the rotational speed of the liquid pump 114 is controlled at the target rotational speed. The process goes back to the step S110 from the step S120B or S130B, to repeat the above operation.

As above, the pressurizing capacity of the liquid pump 114 is increased at the step S120B, so that the pressure P1 at the high pressure side is increased. As a result, the pressure difference ΔP is increased to become close to the predetermined pressure difference ΔPth. The over expansion of the expansion device 112 is likewise prevented, as in the same manner to the second embodiment. And the stable expansion operation can be achieved based on the predetermined pressure difference ΔPth.

When the pressure difference ΔP becomes lower than the predetermined pressure difference ΔPth, exciting current of the electric motor 143 may be decreased to decrease magnetic flux density, as the means for increasing the pressure difference ΔP, in place of the inverter 144 (the means for increasing the number of rotation) of the electric motor 143. Namely, the rotor of the electric motor 143 is formed by an electric coil, the magnetic flux density is decreased by decreasing the exciting current to such electric coil. As a result, the necessary torque for the electric motor 143 is decreased to thereby increase the number of rotation. Accordingly, the pressurizing capacity of the liquid pump 114 is increased so that the pressure difference ΔP can be increased.

(Other Modifications)

In the above embodiments, the pressure sensor 131 on the high pressure side and the pressure sensor 132 on the low pressure side are respectively arranged between the heating device 111 and the expansion device 112 and between the expansion device 112 and the condensing device 113. However, the pressure sensor 131 may be arranged between the liquid pump 114 and the heating device 111, where as the pressure sensor 132 may be arranged between the condensing device 113 and the liquid pump 114.

The expansion device control system of the present invention is applied to the control system for the expansion device 112 for the Rankine cycle 110. However, the control system of the present invention may be applied to a control system for an expansion device for Brayton cycle (a turbine device).

The Rankine cycle 110 is applied to the vehicle, however, it may be used for other industrial purposes. 

1. A waste heat collecting apparatus for a vehicle comprising: an engine cooling circuit, through which engine cooling water is circulated; and Rankine cycle having an expansion device, a condensing device, a refrigerant pump, and a heating device, which are connected in a closed circuit so that refrigerant is circulated in the closed circuit by the operation of the refrigerant pump, wherein the heating device is disposed in the engine cooling circuit for heating the refrigerant of the Rankine cycle with the heat of the engine cooling water, so that the refrigerant is converted to high pressure and high temperature refrigerant, the heating device is connected to an inlet side of the expansion device for supplying the high pressure refrigerant to the expansion device, the condensing device is connected to an outlet side of the expansion device for cooling down and condensing the refrigerant from the expansion device through heat exchange with the ambient air, so that the pressure of the refrigerant at the outlet side of the expansion device depends on a condensing capacity of the condensing device, the expansion device is of a fixed displacement type fluid machine, and an output shaft of the expansion device is driven to rotate by expansion of the refrigerant in a working chamber thereof, the expansion of the refrigerant is performed by a pressure difference of the refrigerant between the high pressure at the inlet side and low pressure at the outlet side of the expansion device, and a volume ratio of expansion for the expansion device is selected at a value, at which proper expansion of the refrigerant is achieved when the pressure difference between the high pressure and the low pressure is minimum.
 2. A waste heat collecting apparatus according to claim 1, further comprising: a refrigerating cycle having a compressor device operatively connected to and driven by an engine, a condenser, and an evaporator, wherein the condensing device of the Rankine cycle is commonly used as the condenser for the refrigerating device.
 3. A waste heat collecting apparatus according to claim 2, wherein the volume ratio of expansion for the expansion device is selected at a value between 1.5 and 2.5.
 4. A waste heat collecting apparatus for a vehicle comprising: Rankine cycle having an expansion device; a condensing device; a refrigerant pump; and a heating device, wherein the expansion device, the condensing device, the refrigerant pump, and the heating device are connected in a closed circuit so that refrigerant is circulated in the closed circuit by the operation of the refrigerant pump, the expansion device generating a rotational driving force by expansion of the refrigerant; an electric power generator operatively connected to the expansion device for generating the electric power when it is driven to rotate by the rotational driving force of the expansion device; a pressure detecting device for detecting a pressure difference of the refrigerant between a pressure at a high pressure side of the expansion device and a pressure at a low pressure side of the expansion device; and a pressure increasing means for increasing the pressure difference when the pressure difference detected by the pressure detecting device is lower than a predetermined pressure difference, so that the pressure difference becomes closer to the predetermined pressure difference.
 5. A rotational force generating apparatus comprising: a high pressure generating device for generating a high pressure of working fluid; a low pressure generating device for generating a low pressure of the working fluid; an expansion device having a fixed displacement and rotating an output shaft by a pressure difference of the working fluid between the high pressure generated by the high pressure generating device and the low pressure generated by the low pressure generating device, wherein a volume ratio of expansion for the expansion device is selected at a value, at which proper expansion of the working fluid is achieved when the pressure difference between the high pressure and the low pressure is minimum.
 6. A rotational force generating apparatus according to claim 5, wherein the high pressure generating device comprises a heating device for heating the working fluid with heat generated from a vehicle.
 7. A rotational force generating apparatus according to claim 6, wherein the high pressure generating device comprises a heating device for heating the working fluid with heat of engine cooling water.
 8. A rotational force generating apparatus according to claim 5, wherein the low pressure generating device comprises a condensing device for cooling down the working fluid by the ambient air, so as to decrease the pressure of the working fluid, and the volume ratio of expansion for the expansion device is selected at a value, at which the proper expansion of the working fluid is achieved during the summer season, during which the pressure generated at the low pressure generating device becomes higher than the pressures in other seasons.
 9. A rotational force generating apparatus according to claim 5, wherein the low pressure generating device comprises a condensing device, which is commonly used for Rankine cycle and a refrigerating cycle, and the volume ratio of expansion for the expansion device is selected at a value between 1.5 and 2.5.
 10. A rotational force generating apparatus according to claim 5, wherein a motor generator is driven by the output shaft to generate the electric power.
 11. A control system for an expansion device comprising: an expansion device for generating a rotational driving force by expansion of high pressure and high temperature working fluid; an electric power generator driven by the rotational driving force of the expansion device; a pressure detecting device for detecting a pressure difference of the working fluid between a pressure at a high pressure side of the expansion device and a pressure at a low pressure side of the expansion device; and a pressure increasing means for increasing the pressure difference when the pressure difference detected by the pressure detecting device is lower than a predetermined pressure difference, so that the pressure difference becomes closer to the predetermined pressure difference.
 12. A control system for an expansion device according to claim 11, wherein the expansion device is of a scroll type device which comprises: a movable scroll to be rotated by the expansion of the working fluid, with respect to a fixed scroll, with an orbital motion; and a crank device provided to the movable scroll for generating the rotational driving force in accordance with the orbital motion of the movable scroll, and the fixed scroll and the movable scroll are pushed to each other, as a function of the crank device, during the expansion of the working fluid.
 13. A control system for an expansion device according to claim 11, wherein the pressure detecting device comprises: a pressure sensor for detecting a high pressure side pressure and a pressure sensor for detecting a low pressure side pressure of the expansion device; and a controller for calculating a difference between the high pressure side pressure and the low pressure side pressure as the pressure difference.
 14. A control system for an expansion device according to claim 11, wherein the pressure increasing means comprises: the electric power generator; and a device for decreasing a number of rotational speed of the electric power generator.
 15. A control system for an expansion device according to claim 14, wherein the device for decreasing the number of rotational speed of the electric power generator is an inverter for controlling the rotational speed of the electric power generator.
 16. A control system for an expansion device according to claim 14, wherein the device for decreasing the number of rotational speed of the electric power generator comprises a magnetic flux density increasing means for increasing the magnetic flux density by increasing excitation of a coil for a rotor of the electric power generator.
 17. A control system for an expansion device according to claim 11, wherein the expansion device is used for Rankine cycle, and the pressure increasing means comprises: a condensing device provided on a low pressure side of the Rankine cycle; and a device for increasing condensing capacity at the condensing device.
 18. A control system for an expansion device according to claim 17, wherein the device for increasing condensing capacity at the condensing device comprises a blower device for blowing air to the condensing device, wherein the blower device increases the amount of the air to the condensing device.
 19. A control system for an expansion device according to claim 11, wherein the expansion device is used for Rankine cycle, and the pressure increasing means comprises: a liquid pump for pressurizing the working fluid in the low pressure side of the Rankine side and for supplying the pressurized working pressure to the high pressure side of the Rankine side; and a device for increasing a rotational speed of the liquid pump.
 20. A control system for an expansion device according to claim 19, wherein the device for increasing the rotational speed of the liquid pump comprises an inverter for controlling a rotational speed of an electric motor for driving the liquid pump.
 21. A control system for an expansion device according to claim 20, wherein the device for increasing the rotational speed of the liquid pump comprises a means for decreasing magnetic flux density of the electric motor for driving the liquid pump by decreasing the excitation for the electric motor. 